Valvular regurgitation (leakage) is a serious life threatening disorder and is associated with a number of cardiac diseases. Present techniques for assessing the severity of leakage are invasive and qualitative. The use of color Doppler echocardiography has provided techniques for duplicating the angiographic grade in a noninvasive fashion, but these empirical techniques are still semi-quantitative at best. The current techniques are not grounded in the physics of the regurgitant jet and tremendous variability exists for Doppler jet images due to physiologic factors. This proposal has three goals. The first is to address the hypothesis that equations can be derived from basic fluid mechanic principles to quantify regurgitant volume using quantities that can be directly measured by Doppler. Second, these basic physical principles will be used to interpret color flow mapping variability related to regurgitant jet behavior in the presence of solid structures or interrupting flows. Third, additional variability inherent to measurement technique (i.e. instrument settings) will be addressed. To achieve these objectives, the following specific aims are proposed: (1) to derive equations from the principles of turbulent jet flow and conservation of mass which provide orifice flow rate, and therefore regurgitant volume, as a function of Doppler measurable quantities; (2) in in vitro models, to test the accuracy of the equations in predicting actual regurgitant volume; (3) to define in an in vitro model, the relationship between regurgitant flow, and spatial characteristics of the color flow jet, namely, jet length, width, area, and volume; (4) in in vitro models, to address the variability in these relationships due to machine settings, driving pressure, and physiologically observed jet flow phenomena, namely, the Coanda effect, impingement, counterflow, and coflow; and (5) to investigate the applicability of the quantitation techniques to various designs of heart valve prostheses.